1. Field of the Invention
The present invention relates to an optical switch for transmitting optical signals and detecting a specific signal and an optical communication system using the optical switch.
2. Description of the Related Art
As an alternative to a telecommunication system for transmitting electric signals, an optical communication system using an optical fiber has recently been put into practical use with a view toward achieving prevention of electromagnetic noise, an increase in transfer capacity, a weight reduction in system, simplification of work, etc.
FIG. 5 is a block diagram showing a conventional optical communication device employed in such a system. This is equivalent to an optical communication system wherein a light-emitting unit 1 is electrically turned on/off to thereby transmit such on/off information to a photo-detector 3 through an optical fiber 2. The light-emitting unit 1 has a light-emitting device 1a comprised of an LED or the like for converting an electric signal into an optical signal, a switch 1b for turning on/off the light-emitting device 1a according to information .left brkt-top.1.right brkt-bot.and .left brkt-top.0.right brkt-bot., and a lens 1c for focusing light emitted from the light-emitting device 1a on an end surface of the optical fiber 2. An electrical switch is used as the switch 1b.
In the optical communication system constructed in this way, the switch 1b performs switching at high speed when an optical signal is subjected to time sharing, followed by transmission from one light-emitting unit 1 to a plurality of photo-detectors 3 on a time-sharing basis. When optical signals are transmitted from a plurality of light-emitting units 1 to a plurality of photo-detectors 3 in a one-to-one correspondence, the plurality of light-emitting units 1 and the plurality of photo-detectors 3 respectively having selectivity with respect to wavelengths .lambda.1, . . . .lambda.n are placed on the optical fiber 2 in a one-to-one correspondence by their wavelength multiplexing.
As such an optical communication system, there is known a system for monitoring or supervising the operations of a plurality of switching devices employed in an automatic vending machine, a plant, etc. or the operations of a plurality of door switches for automobiles.
However, the above-described optical communication system has a problem in that since the light-emitting device 1a in the light-emitting unit 1 on the transmitting side is turned on and off by the switch 1b to generate the optical signal, the life of the light-emitting device la becomes short and the system is low in reliability.
Another problem also arises in that since there is need to supply power to the light-emitting device 1a of the light-emitting unit 1 on the transmitting side, it is necessary to place a power line in the same place in addition to the optical fiber 2, so that the optical communication system cannot take full advantage of their merits such as a weight reduction in system and simplification of work, whereby the optical communication system cannot be applied to a system required at a location placed under hostile environmental conditions apt to cause an explosion or the like.